1. Field of the Invention
The present disclosure relates to a system of controlling a diameter of a single crystal ingot and a single crystal ingot growing apparatus including the same.
2. The Prior Art
In order to manufacture a semiconductor, a wafer needs to be prepared and in order to prepare the wafer, a single crystal needs to be grown in an ingot form. For this, a Czochralski method (hereinafter, a CZ method) may be applied.
Moreover, in order to achieve a high quality of a silicon single crystal ingot, a pull speed correction value is applied through various parameters. Also, various sensors installed at peripheral devices to control an ingot diameter that may affect its quality are configured to realize the uniform diameter. At this point, a Charge-Coupled Device (CCD) camera sensor and an Automatic Diameter Control (ADC) sensor, which are installed at the external of the device, are used for a pull speed and diameter control and a Proportional Integral Derivative controller (PID) controller is used to control information, diameters, and pull speeds, which are obtained from the sensors.
In relation to the CZ method, a single crystal ingot controlling system includes a motor driving unit for changing an actual pull speed to mutually meet a current change amount read from a diameter monitoring system and a target pull speed through operations of the PID controller.
According to a related art, after measuring a diameter of a single crystal using a CCD camera or an ADC sensor, if there is an error between a present value (PV) and a set value (SV), an output of a manipulated value (MV) that changes a pull speed is used in principle for allowing the diameter and the pull speed to reach a standard value. Accordingly, it may be expressed with pull speed control according to a diameter change.
P, I, and D values of the PID controller are components of proportion, integral, and differential and contribute to total output. An output intensity of each component is determined according to setting of the P, I, and D values.
Moreover, an important part of the PID controller is related to an actual value recognizing method. A sampling speed, a period, and a type of a value delivered by a sensor recognizing a diameter for controlling may greatly affect the PID control. Additionally, there are many variables about whether to process or average all raw data or about a period at which sampling is performed.
Additionally, reasonable pre-processing of information from a sensor before tuning of the P, I, and D constant values is required.
Furthermore, in order to obtain a high-quality silicon single crystal of zero-defects or very low defects through the silicon single crystal growing method, it is important to accurately control an actual pull speed with respect to a target pull speed set by V/G, i.e., a ratio of a pull speed V and a single crystal axial direction temperature gradient G.
If the actual pull speed is higher than the target pull speed, there is a vacancy defect such as Flow Pattern Defect (FPD) and on the contrary, if the actual pull speed is lower than the target pull speed, an Oxidation induced Stacking Fault (OISF) region occurs around the crystal and if growth is in progress at a slower speed, an interstitial defect such as Large Dislocation Pit (LDP) occurs. The defect such as OISF may cause fatal device fail during a process of a high-quality wafer such as a rapid thermal processing (RTP) wafer used for a dynamic random access memory (DRAM) or a flash memory according to a recently-reduced design rule. Therefore, in order to manufacture a high quality single crystal including only a remaining vacancy Pv region and a remaining interstitial Pi region, i.e., non-defective regions, accurately controlling of a pull speed is certainly required.